Hydrogen peroxide solutions have been used for many years for a variety of purposes, including bleaching, disinfecting, and cleaning a variety of surfaces ranging from skin, hair, and mucous membranes to contact lenses to household and industrial surfaces and instruments. Unfortunately, unless very stringent conditions are met, hydrogen peroxide solutions begin to decompose into O.sub.2 gas and water within an extremely short time. Typical hydrogen peroxide solutions in use for these purposes are in the range of from about 0.5 to about 6% by weight of hydrogen peroxide in water. The rate at which such dilute hydrogen peroxide solutions decompose will, of course, be dependent upon such factors as pH and the presence of trace amounts of various metal impurities, such as copper or chromium, which may act to catalytically decompose the same. Moreover, at moderately elevated temperatures the rate of decomposition of such dilute aqueous hydrogen peroxide solutions is greatly accelerated. Hence, hydrogen peroxide solutions which have been stabilized against peroxide breakdown are in very great demand.
A large variety of stabilizers have been proposed for use with hydrogen peroxide to deactivate trace catalytic impurities, including stannous salts, ethylene diamine tetracetic acid, and the like.
The primary hydrogen peroxide stabilizer which has been developed and in wide use today is sodium stannate. This stabilizer serves the desired function of substantially reducing hydrogen peroxide decomposition, and is suitable for a number of applications to which such solutions are put. However, sodium stannate preserved hydrogen peroxide solutions cannot be used with high water content ionic lens materials, since a hazing or milky filming of the lens material results.
In an effort to obtain stabilized peroxide solutions for use with such materials, whether as lenses or other fabricated articles, materials such as Dequest.RTM. 2060 (diethylenetriamine penta(methylene phosphonic acid), produced by Monsanto) have been used with hydrogen peroxide.
For example, U.S. Pat. No. 3,860,391 discloses bleacing compositions containing hydrogen peroxide and, as a stabilizer, amino lower alkylene polyphosphates, including diethylene triamine penta (methylenephosphinic acid) or salts thereof, and/or hydroxy alkane phosphates, with or without additional stabilizer constituents, and adjusted to a pH of between about 9.0 and 12.0 with, e.g. sodium hydroxide, for the bleaching of cellulose materials. Exemplified are compositions having a pH of 12.0.
While Dequest.RTM. 2060 is a good hydrogen peroxide stabilizer, it has been found that its protective action is self limiting. Those stabilizers act by chelating metals, which metals catalyze or enhance the peroxide decomposition. However, this stabilizer undergoes changes in peroxide solutions which make it a poor chelator for metals, and hence, the stabilizing effect is dissipated. It is usually added to the non-peroxide components to chelate peroxide decomposing contaminants before the peroxide is added thereto. If it is added to the peroxide portion, the nitrogens in the Dequest.RTM. 2060 become oxidized and the chelating power is lost.
Soft contact lenses are characteristically prepared from hydrophilic polymers, such as polymers of hydroxyethyl methacrylate (HEMA), crosslinked with a conventional crosslinking agent, such as ethylene glycol dimethacrylate (EGDMA), or more complex copolymer systems including copolymers of HEMA, EGDMA, methacrylic acid and/or poly-N-vinylpyrrolidone, and the like. Other hydrophilic monomers conventionally employed in varying amounts in the manufacture of soft contact lenses include, for example, N-vinylpyrrolidone, glyceryl methacrylate, diethylene glycol monomethacrylate, triethylene glycol monomethacrylate, allyl 2-hydroxyethyl ether, acrylic acid, acrylamide, N,N-dimethylacrylamide, and the like. Other conventional crosslinking agents commonly employed include, inter alia, diallyl ether, divinyl benzene, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, diallyl succinate, allyl methacrylate, glycerin tri-methacrylate, and the like. Moreover, various amounts of relatively hydrophobic monomer units can be employed in the manufacture of soft contact lens materials, as long as the final copolymer network exhibits the desired hydrophilic characteristics. Typical hydrophobic monomers include methyl methacrylate, glycidyl methacrylate, N-(1,1-dimethyl- 3-oxobutyl)acrylamide, siloxane methacrylates, perfluoroalkyl methacrylates, perfluoroalkoxyperfluoroalkyl methacrylates, and the like. In general, such lenses exhibit marked hydrophilic properties and, when wet, absorb water and are soft and flexible.
While these lenses are not actually perforate, they do have a sufficient degree of molecular porosity to permit water, oxygen and tear fluids to permeate the lens structure. In order for the disinfection of such lenses to be effective after they have been worn, it is important that contaminants be removed from both surfaces, and the interior of the lens, to the extent contaminants are present therein. Hydrogen peroxide in the form of a dilute solution, e.g. about 0.5 to 6% by weight in water, is known to be effective for use with contact lenses in order to kill any contaminating microorganisms.
Unfortunately, the highly basic compositions indicated above are undesirable in a contact lens environment, especially in the disinfection of contact lenses, and in uses of hydrogen peroxide where the composition directly contacts skin, mucous membranes, or instruments made of contact lens polymer materials and subsequently are used on or in the body.
The above difficulties and growing importance of peroxide as a disinfectant for contact lens materials makes it imperative that a suitable peroxide stabilizer be found.